When a rear end of a vehicle collides with another vehicle running from backward (rear end collision), a body of an occupant is strongly pushed to a seatback. At the same time, a head (neck) of the occupant is bent backward largely and carried upward. After that, the body and the head of the occupant are forced to fall forward by counter force suddenly. Thus, at the time of the rear end collision, when sudden force is applied, in particular, to the head, even when the force is not so strong, there can be a possibility for the occupant to be whiplashed. Accordingly, in particular, a function for inhibiting a backward bend of a head of an occupant that is caused by the rear end collision is desired for a headrest.
For inhibiting whiplash of an occupant by a rear end collision, it is desirable that a headrest moves immediately and appropriately to receive an entire region from a head to a neck of the occupant with reliability when the rear end collision occurs, or when the rear end collision is predicted.
JPH11-334439A (document 1) describes a conventional headrest provided at a seat for a vehicle. In this headrest, when the vehicle predicts or detects a rear end collision, a receive portion for receiving a head of an occupant sitting on the seat is moved diagonally upward to protect the head of the occupant. Such headrest is so called an active headrest. According to the document 1, the headrest includes a drive motor therein. The vehicle includes a sensor for predicting or detecting a rear end collision. Here, when a central processing unit (CPU) serving as a control means receives a signal notifying that the sensor predicts or detects a rear end collision, the CPU actuates the drive motor in the headrest. By the action of the drive motor, the headrest tilts diagonally upward. The tilted posture of the headrest protects the head of the occupant and inhibits whiplash of the occupant.
JP2003-70591A (document 2) describes another conventional headrest including an expansion portion for protecting a head of an occupant. In the headrest according to document 2, when the vehicle predicts or detects a rear end collision, air is supplied to the expansion portion by an air compressor to expand the expansion portion thereby to protect the head of the occupant and inhibit whiplash of the occupant.
JPH8-187139A (document 3) describes still another conventional headrest including a contact pressure sensor for detecting a contact pressure applied from a head of an occupant. In the headrest according to document 3, the headrest is driven and controlled so that a constant contact pressure can be applied to the headrest from the head of the occupant. When a rear end collision is predicted on the basis of change of the contact pressure from the head of the occupant, the headrest becomes a state in which the headrest is fixed. By doing so, the headrest can receive the head bent by the rear end collision, and can inhibit whiplash of the occupant.
In the headrest according to document 1, when the vehicle predicts or detects a rear end collision of the vehicle, the headrest tilts so that a lower portion of the headrest protrudes to an occupant side. Such tilt motion of the headrest might be effective only in a limited condition, for example, in a rear end collision at low speed. However, in a case where shock of a rear end collision is particularly large, the head of the occupant is bent backward largely. If the headrest tilts in such a case, a neck of the occupant is pressed by the protruding lower portion of the headrest. Accordingly, such tilt motion would be dangerous rather than effective. Therefore, such headrest of a tilt type would cause high risk of whiplash of an occupant.
In the headrest according to document 2, the air compressor blows air into the expansion portion. Accordingly, a certain length of time is necessary for sufficiently filling the expansion portion with air after the vehicle predicts or detects a rear end collision. Therefore, it is difficult to inhibit whiplash of the occupant with reliability by such a type of headrest with an expansion portion at the time of an instantaneous occurrence of a rear end collision of the vehicle.
In the headrest according to document 3, when the collision sensor equipped with a vehicle detects a rear end collision of the vehicle, the headrest is fixed to a supporting posture. In other words, the headrest does not receive the head of the occupant actively. Accordingly, the headrest cannot contact with a back of the head with reliability when the head of the occupant is bent backward by shock of the rear end collision. Further, because the headrest includes the contact pressure sensor, or the like, for detecting the contact pressure from the head, a configuration of the headrest tends to be complex and large in size. As a result, manufacturing cost tends to be high.
A need thus exists for a headrest which can move quickly and protect a head of an occupant with reliability when a vehicle predicts or detects a rear end collision of the vehicle. The present invention has been made in view of the above circumstances and provides such a headrest.